title: Surface diffusion experiments with STM: equilibrium correlations and non-equilibrium low temperature growth.
abstract: Measurements of surface diffusion depend on the state of the system whether the state is equilibrium versus non-equilibrium. Equilibrium experiments carried out in 2-d overlayers measure the collective diffusion coefficient D(c) and can test theoretical predictions in two-dimensional statistical mechanics. Growth experiments typically carried out at low temperatures and/or high flux rates probe systems under non-equilibrium conditions where novel diffusion mechanisms can potentially exist. The use of STM to study both types of measurements is discussed. D(c) can be measured from the autocorrelation of time-dependent tunneling current fluctuations generated by atom motion in and out of the tunneling area. Controlled experiments as function of temperature, coverage and tip-surface separation confirm that the signal is diffusive. For growth experiments the unusually uniform height island (for Pb/Si(111) In/Si(111)) has revealed a novel and intriguing type of diffusion at low temperatures that accounts for the high degree of the self organization. By monitoring the evolution of the stable islands out of a mixture of stable and unstable islands the unusual role of the wetting layer surrounding the growing islands is revealed.
authors.affiliation: Ames Laboratory-USDOE, Iowa State University, Ames, IA 50011, USA.
authors.forename: M C
authors.initials: MC
authors.lastname: Tringides
authors.forename: M
authors.initials: M
authors.lastname: Hupalo
mesh_terms: D003080:Cold Temperature; D004058:Diffusion; D004553:Electric Conductivity; D057927:Hydrophobic and Hydrophilic Interactions; D007204:Indium / Q000737:chemistry*; D007854:Lead / Q000737:chemistry*; D016252:Microscopy, Scanning Tunneling / Q000295:instrumentation* / Q000379:methods; D012825:Silicon / Q000737:chemistry*; D013499:Surface Properties; D055471:Thermal Diffusion
chemical_list: D007204:Indium; D007854:Lead; D012825:Silicon